The objectives are to study the development of sustained, endogenous attention in young infants, and to relate developmental trends in sustained attention to concurrent heart rate (HR) changes. The specific aims are: 1) To study sustained, subject-controlled attention in infants from 8 to 26 weeks of age, and to study the control of saccadic and smooth pursuit eye movements during heart-rate-defined attention phases, in order to infer the neuro-developmental systems controlling attention- directed eye movements during attention; and 2) To study individual differences in respiratory sinus arrhythmia (RSA; variability in HR occurring at the respiration frequency) with respect to individual differences in sustained attention, premature and full-term recognition memory differences, and sleep assessment of RSA. The research may provide a "model preparation" for the study of pathological patterns of infant attention found in high-risk premature infants, and for the later development of attentional disabilities found in hyperactive, autistic, and retarded children. Infants will be tested from 8 to 26 weeks of age. HR and respiration will be measured during a five minute baseline, and during attention. Four experiments will study sustained attention in light of other attention phases. Experiment 1 will examine the blink reflex, an example of an early phase of information processing, in different attention phases. Experiments 2 and 3 will examine peripheral stimulus localization as a function of sustained attention. Experiment 4 will study the relation of attention to smooth pursuit and saccadic eye movements during visual tracking. Two experiments will emphasize individual differences in sustained attention related to RSA. Experiment 5 will examine the retrieval aspect of infant recognition memory in preterm infants, who are known to have recognition memory and sustained attention deficits. Experiment 6 will examine the longitudinal stability of HR, respiration, and RSA during sleep states, and the relation of those measures to sustained attention. It is predicted that 1) sustained attention will show age and individual differences, whereas other attention types will not; 2) developmental changes in sustained attention will differentially affect behavioral systems, including recognition memory in the paired-comparison paradigm, and different eye movement systems.